Preheat the oven to 180 ° C.
Melt the dark chocolate and the butters in a double boiler.
In a bowl, beat the eggs and erythritol until a frothy mixture is obtained. Stir in the almond flour, vanilla extract and salt.
Incorporate the chocolate / butters mixture until a homogeneous mixture is obtained.
Half-fill the muffin cups (previously buttered if necessary) with the preparation.
Melt the white chocolate in the microwave.
Place the white chocolate in the molds then cover with the dark chocolate preparation.
Bake 9 minutes at 180 ° C. To obtain a less runny heart, just cook for 3 more minutes.